1. Field of the Invention
The present invention relates to concrete floors for buildings or similar structures which utilize at least one precast reinforced concrete slab as a basic structural element.
2. Description of the Prior Art
In a conventional method of constructing a floor for buildings or similar structures which utilizes precast reinforced concrete slabs, one or more such slabs are placed on a supporting structure, which may be two or more steel or concrete beams or girders, to form a basic floor structure. Reinforcing steel bars are placed under tension above the slab, a ready mixed concrete is poured in-situ on the slab to embed the reinforcing steel bars, and the poured concrete or so-called cast-in-place concrete is cured to form a floor structure composite with said precast slab.
It is known that, in general, the strength of a floor of a predetermined concrete material is in proportion to the square of the thickness in the floor.
In a floor formed according to said conventional methods, the strength thereof can be calculated based on the total thickness of the floor if the slab is made composite with the cast-in-place concrete. If the cast-in-place concrete does not act compositely with the precast reinforced concrete slab, the strength is calculated using the thickness of the slab and the subsequently formed concrete layer individually.
It can be seen from experience that more pouring and curing of the ready mixed concrete in-situ on the precast concrete slab does not provide sufficient composite action therebetween. This means the thickness of the precast slab or the cast-in-place concrete layer must be increased to achieve the same strength as the composite slab, but this has the disadvantage of increasing the floor weight.
In order to resolve such a problem, another type of precast reinforced concrete slab and an apparatus for manufacturing the same have been proposed as disclosed in U.S. Pat. No. 3,426,403, wherein at least one lattice girder is arranged in position in a mold, if necessary together with reinforcing steel bars. Ready mixed concrete is poured in the mold and cured to form a solidified concrete slab having a projection which is a part of said lattice girder. The lattice serves as an anchor when this concrete slab is placed in position and ready mixed concrete is poured and cured thereon to construct a floor structure. An apparatus for manufacturing a lattice girder different from that shown in said U.S. Pat. No. 3,426,403 has been disclosed in U.S. Pat. No. 3,198,219.
Such a precast reinforced concrete slab is called "Omnia Slab" or "Kaiser Plate" and is employed widely as a base element to be used compositely with cast-in-place concrete to form a so-called composite floor structure for concrete buildings or similar structures. The slab has such disadvantages, due to its structure having part of the lattice girder project from the reinforced concrete slab, as continuous molding cannot be carried out, a higher manufacturing cost, and careful handling is required in storage, transportation, and installation to reduce workability, since the projecting lattice girder tends to deform due to impact or like external causes.